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2005
Pyridine derivatives
R 0380
C(6)-Alkylation of 3-Hydroxypiperidine via Reductive and Homolytic Cleavage
N,S-Acetals. — The desired precursor acetal (II) for the title reaction is prepared
18- 131 of
from piperidine (I) via anodic oxidation in MeOH followed by exposure of resulting
N,O-acetals to thiophenol. Reductive lithiation of acetal (II) is achieved using BuLi followed by Li naphthalide. Addition of appropriate electrophiles to the putative α-lithiated piperidine intermediate gives the target piperidines predominantly as trans-isomers. Since an excess of Li naphthalide is required, the method is limited to electrophiles that do not undergo competitive reactions with this reagent. Acetal (II) also undergoes homolytic cleavage of the C—S bond and trapping of the resulting radical by
alkenes provides an alternative entry to title compounds. In this case, ca. 1:1 mixtures
of separable cis and trans isomers are formed. — (BARTELS, M.; ZAPICO, J.;
GALLAGHER*, T.; Synlett 2004, 14, 2636-2638; Sch. Chem., Univ. Bristol,
Cantock's Close, Bristol BS8 1TS, UK; Eng.) — Klein
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